Lead-in bushing



N, R. SMITH LEAD-IN BUSHING April 7, 1936.

Filed April 2, 1935 INVENTOR NEWELL R. SMITH '1 flfilko/ ATTORNEY Patented Apr. 7, 1936- UNITED STATES PATENT OFFICE LEAD-IN BUSHING Application April 2, 1935, Serial a... 14.205

5 Claims.

My invention relates to radio receiving tubes of the type having a metal envelope, and is particularly concerned with the lead-in construction at the top of the envelope.

In the manufacture of all-metal tubes of the screen grid type, one of the external connections is usually made through an insulating bushing at the top of the envelope remote from the base. This bushing must not only properly insulate the lead-in from the metal envelope, but must also support a contactor and lead from associated apparatus to the tube.

' It is accordingly an object of my invention to provide an insulating bushing that is electrically eflicient and mechanically strong.

A further object of my invention is to provide an insulating lead-in bushing at the top of an all-=metal tube which is rugged in construction, simple in manufacture and neat in appearance.

A fuller understanding of my invention may be had by referring to the accompanying drawing which shows the upper end of the metal envelope discharge device with a sectional view of a top lead-in bushing.

Referring to the drawing, l designates an inverted cup-shaped metal envelope within which may be sealed any desired arrangement of electrodes. One of the electrodes, a grid by way of example, is shown with its lead extending through the upper end of the envelope. In applying my invention to this form of tube i prefer to insulate the grid lead from the envelope by welding the lower flange of a short tabulation or eyelet 3 to the envelope in registry with a small perforation in the upper end of the envelope. The grid lead is sealed gas-tight into the eyelet 3 by a bead 4 of insulation such as glass. [it the upper end of the envelope is a shallow cupshaped metal extension shown by way of exam-- ple as a member 5 having a flange The extension may, if desired, be formed integral with the envelope material or formed as a separate member suitably secured as by a welded or brazed joint l to the flat portion of the upper end of the envelope. Seated within the flange of the cup-shaped member 5 is a disc of ins -ationv S, which is secured in place by rolling or iol over the upper edge of the flange l, as ShOl 9. Insulating disc 8 has a central opening, fits over and in spaced relation with the tubular .eyelet As shown, the opening in the ing disc 8 is closed by an inverted thimble or cup= shaped member ill mechanically secured in the opening by flanges ii. A solid electrical bond is made between the grid lead wire and the thim ble member Ill by flowing molten solder or other conductive adhesive l2 into the end of the thimble member. Electrical connection to the grid of the tube may be made by fricticnally engaging the thimble member il with the conventional 5 form of spring tensioned contact clip.

The sides of the cup-shaped member 5 may be formed with straight or vertical walls and the insulating disc 8 spaced from the bottom thereof by means of a thin metal ring fitted under the 10 disc, or the disc may be formed with a downwardly extending flange around its lower edge, or the cup-shaped member may be pressed out with raised portions in its bottom. Any of the mentioned modifications may serve to properly if) space the disc 8 above the bottom of its holder it will be obvious to those skilled in the art that 1 various other modifications may be made in my device without departing from the spirit there of. It is accordingly desired that my invention 20 be limited only by the prior art and by the ac companying claims.

l. claim:

1. A thermionic discharge device comprising a metal envelope having a perforation, a tubular 25 eyelet secured gas-tight to said envelope in reg istry with said perforation, insulation sealing an electrode lead into said tubular eyelet, a shallow cup-shaped member secured at its bottom to said envelope and around said tubular eyelet, an insulating disc with an outwardly exten metal thimble secured to the upper rim of cup-shaped member, and means electricallyj ing the electrode lead to said metal thimble.

2. A thermionic discharge device comprising a metal envelope containing cathode, grid anode electrodes, means insulatingly securing a lead to one of said electrodes through the wal of said envelope comprising an outwardly ex tending tubular eyelet secured in a gas-tigh; manner over an opening in said envelope, insulating means sealing said lead-in in tubular member, a metal disc secur to said envelope about said outwardly eaten said disc having an upwardly a centrally recessed insulating folded-over portions of said. vertecl thimlole secured in said recess and over said tubular eyelet, and a conductive adhesive electrically joining the lead-in wire to said thinible.

3. An electron discharge device coinprning metal envelope, a lead-in wire or g thra perforation in said envelope, sealing in a gas-tight manner the wire in perforation, a cup-shaped terminal holder with a perforated bottom fitted over said insulating means and secured at its bottom to said envelope, and insulating disc with a central opening secured in the upper edge 01' said cup-shaped terminal holder. and a terminal member fixed in said opening and electrically connected to said lead-in wire.

4. A thermionic discharge device comprising a metal envelope having a perforation at one end, a tubular eyelet secured gas-tight to said envelope in registry with said perforation, insulation sealing an electrode lead into said tubular eyelet, a cup-shaped metal extension at said end or the envelope around said tubular eyelet, an insulating disc with an outwardly extending metal thimble secured to the upper rim of said aoaaoss cup-shaped extension, and means electrically joining the electrode lead to said metal thimble. 5. A thermionic discharge device comprising a metal envelope with a cup-shaped extension containing cathode, grid. and anode electrodes, means insulatingly securing a lead to one of said electrodes through the wall of said envelope comprising an outwardly extending tubular eyelet secured in a gas-tight manner in an opening in said envelope, insulating means sealing said lead-in wire to said tubular member, an inverted thimble internally connected to said lead-in wire and secured in position over said tubular eyelet by an insulating disc held in spaced relation to said envelope by the rim 0! said cup-shaped extension of the envelope.

. NEWELL B. SMITH. 

